首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
提出了拉格朗日高阶中心型守恒气体动力学格式。用产生于当前时刻子网格密度和当前时刻网格声速的子网格压力构造了子网格力,用加权本质无震荡方法构造的高阶子网格力构造了高阶空间通量,借助时间中点通量的泰勒展开完成了高阶时间通量离散,利用动量守恒条件使得格点速度以与网格面的数值通量相容的方式计算。编制了拉格朗日高阶中心型守恒气体动力学格式,对Saltzman活塞问题进行了数值模拟,数值结果表明,拉格朗日高阶中心型守恒气体动力学格式的有效性和精确性.  相似文献   

2.
The Arbitrary Lagrangian Eulerian (ALE) framework coupled with some boundary tracking techniques is proven to be an effective method for simulation of free‐surface flows. In this paper, a special ALE framework is derived with clarification of three velocities, the notion of mesh‐frozen and field‐frozen, and the notion of tentatively inertial coordinates. A weighted integral ALE governing equations are formulated on generic coordinates and discretized with a finite element method and linear implicit time scheme. The system is solved with a discrete operator splitting technique and superposition‐based logistic parallelization. The formulation and implementation are verified through several fixed‐geometry problems and a reasonably good parallel performance is observed. Capillary jet flow is the main problem of the paper and the numerical techniques for boundary tracking are elaborated, which include an indirect boundary tracking of flux method and an iterative direct boundary tracking method. Also, a high‐order compact scheme for dynamic boundary condition and a squeeze technique for kinematic boundary condition are adopted. The axisymmetric jet breakup is studied in detail and numerical results match with the published data very well. Numerical accuracy and sensitivity are studied, including effects of element type, time scheme, compact scheme, and boundary tracking techniques. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

3.
A one-dimensional transport test applied to some conventional advective Eulerian schemes shows that linear stability analyses do not guarantee the actual performances of these schemes. When adopting the Lagrangian approach, the main problem raised in the numerical treatment of advective terms is a problem of interpolation or restitution of the transported function shape from discrete data. Several interpolation methods are tested. Some of them give excellent results and these methods are then extended to multi-dimensional cases. The Lagrangian formulation of the advection term permits an easy solution to the Navier-Stokes equations in primitive variables V, p, by a finite difference scheme, explicit in advection and implicit in diffusion. As an illustration steady state laminar flow behind a sudden enlargement is analysed using an upwind differencing scheme and a Lagrangian scheme. The importance of the choice of the advective scheme in computer programs for industrial application is clearly apparent in this example.  相似文献   

4.
This paper is concerned with the numerical prediction of the extrudate swell behaviour of branched polymer melts in a planar configuration. The multi-mode extended pom-pom (XPP) model is used to describe the polymer dynamics. A second-order operator-integration-factor splitting scheme is used for the temporal discretisation of the problem, whilst a spectral element scheme is used in space. The free surface is evolved in a Lagrangian manner using the third-order conditionally stable Adams–Bashforth method. A thorough mesh convergence study is performed with respect to the temporal and spatial discretisation parameters. The influence of the nature of the discrete relaxation spectrum on the swelling ratio and as an indicator of polydispersity is investigated. The predictions of numerical simulations are also compared with a selection of experimental results from the literature. The parameters in the XPP model are determined from rheological data. Good agreement is obtained for branched low-density polyethylenes. The ability to model a melt with a high molecular weight tail using a discrete relaxation spectrum for which the largest relaxation time is isolated from the others is also investigated.  相似文献   

5.
大变形问题分析的局部Petrov-Galerkin法   总被引:2,自引:1,他引:1  
在微机电系统(MEMS)的建模和模拟研究中,大变形或大移动要充分予以考虑.用有限元法分析这类问题,由于难以避免的网格畸变,使模拟效率精度降低甚至失效,无网格方法(Meshless Method)则能在分析这类问题时显示出明显的优势,无网格局部Petrov-Galerkin(MLPG)法被誉为是一种有发展前景的真正无网格法.本文进一步发展了MLPG法,通过对任意的离散分布节点采用局部径向基函数构造插值形函数和Heaviside权函数,分析方程采用局部加权弱形式离散,建立了变量仅依赖于初始构型的完全Lagrange分析格式,最后用Newton-Raphson法迭代求解.文中分析了悬臂梁典型算例和微机电开关非线性大变形问题,通过与有限元结果的比较,表明本文提出的大变形问题无网格局部Petrov-Galerkin法具有稳定性好及收敛性快等优点.  相似文献   

6.
In this paper we extend the non‐staggered version of the central NT (Nessyahu–Tadmor) scheme to the balance laws with geometrical source term. This extension is based on the source term evaluation that includes balancing between the flux gradient and the source term with an additional reformulation that depends on the source term discretization. The main property of the scheme obtained by the proposed reformulation is preservation of the particular set of the steady‐state solutions. We verify the improved scheme on two types of balance laws with geometrical source term: the shallow water equations and the non‐homogeneous Burger's equation. The presented results show good behaviour of the considered scheme when compared with the analytical or numerical results obtained by using other numerical schemes. Furthermore, comparison with the numerical results obtained by the classical central NT scheme where the source term is simply pointwise evaluated shows that the proposed reformulations are essential. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
The kernel gradient free (KGF) smoothed particle hydrodynamics (SPH) method is a modified finite particle method (FPM) which has higher order accuracy than the conventional SPH method. In KGF‐SPH, no kernel gradient is required in the whole computation, and this leads to good flexibility in the selection of smoothing functions and it is also associated with a symmetric corrective matrix. When modeling viscous incompressible flows with SPH, FPM or KGF‐SPH, it is usual to approximate the Laplacian term with nested approximation on velocity, and this may introduce numerical errors from the nested approximation, and also cause difficulties in dealing with boundary conditions. In this paper, an improved KGF‐SPH method is presented for modeling viscous, incompressible fluid flows with a novel discrete scheme of Laplacian operator. The improved KGF‐SPH method avoids nested approximation of first order derivatives, and keeps the good feature of ‘kernel gradient free’. The two‐dimensional incompressible fluid flow of shear cavity, both in Euler frame and Lagrangian frame, are simulated by SPH, FPM, the original KGF‐SPH and improved KGF‐SPH. The numerical results show that the improved KGF‐SPH with the novel discrete scheme of Laplacian operator are more accurate than SPH, and more stable than FPM and the original KGF‐SPH. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
In this article, we propose a simple area‐preserving correction scheme for two‐phase immiscible incompressible flows with an immersed boundary method (IBM). The IBM was originally developed to model blood flow in the heart and has been widely applied to biofluid dynamics problems with complex geometries and immersed elastic membranes. The main idea of the IBM is to use a regular Eulerian computational grid for the fluid mechanics along with a Lagrangian representation of the immersed boundary. Using the discrete Dirac delta function and the indicator function, we can include the surface tension force, variable viscosity and mass density, and gravitational force effects. The principal advantage of the IBM for two‐phase fluid flows is its inherent accuracy due in part to its ability to use a large number of interfacial marker points on the interface. However, because the interface between two fluids is moved in a discrete manner, this can result in a lack of volume conservation. The idea of an area preserving correction scheme is to correct the interface location normally to the interface so that the area remains constant. Various numerical experiments are presented to illustrate the efficiency and accuracy of the proposed conservative IBM for two‐phase fluid flows. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

9.
弹性力学问题的局部Petrov—Galerkin方法   总被引:50,自引:2,他引:48  
龙述尧 《力学学报》2001,33(4):508-518
提出了弹性力学平面问题的局部Petrov-Galerkin方法,这是一种真正的无网格方法。这种方法采和移动最小二乘近似函数作为试函数,并且采用移动最小二乘近似函数的权函数作为加权残值法加权函数;同时这种方法只包含中心在所考虑点处的规则局部区域上以及局部边界上的积分,所得系统矩阵是一个带状稀疏矩阵,该方法可以容易推广到求解非线性问题以及非均匀介质的力学问题。还计算了两个弹性力学平面问题的例子,给出了位移和能量的索波列夫模及其相对误差。所得计算结果证明:该方法是一种具有收敛快、精度高、简便有效的通用方法;在工程中具有广阔的应用前景。  相似文献   

10.
A numerical simulation based on a combined Euler and Lagrange method is investigated in this work to simulate the flow and migration of nanoparticles in a single channel. The motion of discrete nanoparticles is determined by the Lagrangian trajectory method based on the Newton’s second law that includes the influence of the body force, various hydrodynamic forces, the Brownian motion and the thermophoresis force. The coupling of discrete particles with continuous flow is realized through the modification of the source term of the continuous equation. The results reveal the two-phase flow nature of nanoparticle suspensions and their implications to the convective heat transfer of nanofluids.  相似文献   

11.
粘性流体中弹性板振动的有限元耦合问题   总被引:1,自引:0,他引:1  
流体-结构耦合作用问题是工程中比较常见的问题,具有重要意义,由于流体计算的复杂性,迄今为止,大部分的流体-结构耦合分析都是建立在对流体充分简化的基础上,尤其是将流体视为无粘、无旋的理想流体。该文在近年来前人工作的基础上,发展了一种流体-弹性结构耦合计算模式。流体视为不可压、有粘的介质,流场没有自由表面。该文采用SU/PG方法形成流体的有限元方程,采用ALE格式处理流体和结构之间的移动界面。采用预估  相似文献   

12.
This paper presents a Lagrangian cell-centered conservative gas dynamics scheme. The piecewise constant pressures of cells arising from the current time sub-cell densities and the current time isentropic speed of sound are introduced. Multipling the initial cell density by the initial sub-cell volumes obtains the sub-cell Lagrangian masses, and dividing the masses by the current time sub-cell volumes gets the current time sub-cell densities. By the current time piecewise constant pressures of cells, a scheme that conserves the momentum and total energy is constructed. The vertex velocities and the numerical fluxes through the cell interfaces are computed in a consistent manner due to an original solver located at the nodes. The numerical tests are presented, which are representative for compressible flows and demonstrate the robustness and accuracy of the Lagrangian cell-centered conservative scheme.  相似文献   

13.
水陆两栖飞机波浪水面上降落耐波性数值分析   总被引:1,自引:0,他引:1  
在规定的气象水文条件下,水陆两栖飞机起飞和降落的能力是决定其性能的重要因素,即耐波性能。采用ALE方法对流体域进行描述,运用基于微幅波理论的动边界数值造波方法模拟了不同波高和不同波长的动态海平面波浪,通过添加质量阻尼的消波方法抑制了固壁边界反射波对造波结果的影响,并采用罚函数耦合方法描述飞机与水体的耦合作用,研究了水陆两栖飞机在不同海情条件下波浪面上降落的纵摇运动、升沉运动以及底部压力等运动学和动力学特性,分析了水陆两栖飞机入水波浪的波长及波高对水陆两栖飞机耐波性能的影响,为飞机结构设计、水上降落操作规则制订及水陆两栖飞机耐波性物理水池试验提供参考。  相似文献   

14.
A rigorous model of the fully elliptic flow over the blade-to-blade stream surface in an annular aerofoil cascade is developed. The model accuracy stems from its precise simulation of the meridional hub-to-casing flow effects, including those of the shear stress components that are created by the spanwise velocity gradients. These stresses are unprecedentedly introduced in the flow-governing equations in the form of source terms and are modelled as such. The final set of flow-governing equations are solved using the Galerkin weighted residual method coupled with a biquadratic finite element of the Lagrangian type. The flow solution is verified against the numerical results of a fully three-dimensional flow model and a set of experimental data, both concerning a low-aspect-ratio stator of an axial flow turbine under a low Reynolds number and subsonic flow operation mode. The numerical results in this case show well predicted aerofoil loading and pitch-averaged exit flow conditions. Also evident is a substantial capability of the analysis in modelling such critical regions as the wake subdomain. It is further proven that the new terms in the governing equations enhance the quality of the numerical predictions in this class of flow problems.  相似文献   

15.
On the basis of the work [P.‐H. Maire, R. Abgrall, J. Breil, J. Ovadia, SIAM J. Sci. Comput. 29 (2007), 1781–1824], we present an entropy fixed cell‐centered Lagrangian scheme for solving the Euler equations of compressible gas dynamics. The scheme uses the fully Lagrangian form of the gas dynamics equations, in which the primary variables are cell‐centered. And using the nodal solver, we obtain the nodal viscous‐velocity, viscous‐pressures, antidissipation velocity, and antidissipation pressures of each node. The final nodal velocity is computed as a weighted sum of viscous‐velocity and antidissipation velocity, so do nodal pressures, whereas these weights are calculated through the total entropy conservation for isentropic flows. Consequently, the constructed scheme is conservative in mass, momentum, and energy; preserves entropy for isentropic flows, and satisfies a local entropy inequality for nonisentropic flows. One‐ and two‐dimensional numerical examples are presented to demonstrate theoretical analysis and performance of the scheme in terms of accuracy and robustness.Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
Sedimentation of particles in an inclined vessel is predicted using a two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Mapping particle properties to an Eulerian grid and then mapping back computed stress tensors to particle positions allows a complete solution of sedimentation from a dilute mixture to close-pack. The solution scheme allows for distributions of types, sizes and density of particles, with no numerical diffusion from the Lagrangian particle calculations. The MP-PIC solution method captures the physics of inclined sedimentation which includes the clarified fluid layer under the upper wall, a dense mixture layer above the bottom wall, and instabilities which produce waves at the clarified fluid and suspension interface. Measured and calculated sedimentation rates are in good agreement.  相似文献   

17.
A coupled Lagrangian interface‐tracking and Eulerian level set (LS) method is developed and implemented for numerical simulations of two‐fluid flows. In this method, the interface is identified based on the locations of notional particles and the geometrical information concerning the interface and fluid properties, such as density and viscosity, are obtained from the LS function. The LS function maintains a signed distance function without an auxiliary equation via the particle‐based Lagrangian re‐initialization technique. To assess the new hybrid method, numerical simulations of several ‘standard interface‐moving’ problems and two‐fluid laminar and turbulent flows are conducted. The numerical results are evaluated by monitoring the mass conservation, the turbulence energy spectral density function and the consistency between Eulerian and Lagrangian components. The results of our analysis indicate that the hybrid particle‐level set method can handle interfaces with complex shape change, and can accurately predict the interface values without any significant (unphysical) mass loss or gain, even in a turbulent flow. The results obtained for isotropic turbulence by the new particle‐level set method are validated by comparison with those obtained by the ‘zero Mach number’, variable‐density method. For the cases with small thermal/mass diffusivity, both methods are found to generate similar results. Analysis of the vorticity and energy equations indicates that the destabilization effect of turbulence and the stability effect of surface tension on the interface motion are strongly dependent on the density and viscosity ratios of the fluids. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

18.
Vortex methods have found wide applications in various practical problems. The use of vortex methods in free surface flow problems, however, is still very limited. This paper demonstrates a vortex method for practical computation of non-linear free surface flows produced by moving bodies. The method is a potential flow formulation which uses the exact non-linear free surface boundary condition at the exact location of the instantaneous free surface. The position of the free surface, on which vortices are distributed, is updated using a Lagrangian scheme following the fluid particles on the free surface. The vortex densities are updated by the non-linear dynamic boundary condition, derived from the Euler equations, with an iterative Lagrangian numerical scheme. The formulation is tested numerically for a submerged circular cylinder in unsteady translation. The iteration is shown to converge for all cases. The results of the unsteady simulations agree well with classical linearized solutions. The stability of the method is also discussed.  相似文献   

19.
This paper presents a new method for topology optimization of geometrical nonlinear compliant mechanisms using the element-free Galerkin method (EFGM). The EFGM is employed as an alternative scheme to numerically solve the state equations by fully taking advantage of its capability in dealing with large displacement problems. In the meshless method, the imposition of essential boundary conditions is also addressed. The popularly studied solid isotropic material with the penalization (SIMP) scheme is used to represent the nonlinear dependence between material properties and regularized discrete densities. The output displacement is regarded as the objective function and the adjoint method is applied to finding the sensitivity of the design functions. As a result, the optimization of compliant mechanisms is mathematically established as a nonlinear programming problem, to which the method of moving asymptotes (MMA) belonging to the sequential convex programming can be applied. The availability of the present method is finally demonstrated with several widely investigated numerical examples.  相似文献   

20.
不完全膨胀超声速射流的势核中会产生准周期的激波栅格结构, 其与剪切层内拟序结构的相互作用会产生激波噪声. 啸声是主要向上游方向传播的、具有离散频率的高强度激波噪声, 其产生是受一种非线性的声反馈环机制驱动. 精确定位啸声的声源位置是定量理解啸声反馈环机制和发展准确的啸声预测模型的一个关键所在. 为了分析近场啸声, 本文采用高精度数值方法直接求解轴对称可压缩Navier-Stokes方程, 数值模拟了完全膨胀射流马赫数为1.10和1.15的圆形声速喷管欠膨胀超声速冷射流, 得到了A1和A2两种轴对称模态啸声. 通过傅里叶模态分解、本征模态分解和动态模态分解, 分析了射流时序压力场和速度场, 研究了啸声关联拟序流动结构的空间演化, 精确定位了轴对称模态啸声的声源位置. 研究表明: 啸声关联拟序流动结构存在饱和态区域, 啸声声波是在其饱和态区域产生并向外传播; 在本文所涉及的射流马赫数范围内, A1和A2两种轴对称模态啸声的有效声源位置分别是在第4和第3个激波栅格结构的尾缘.   相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号